Bearing arrangement for the support of an exhaust gas turbocharger shaft of an exhaust gas turbocharger

Abstract

A bearing arrangement (14, 16) for supporting an exhaust gas turbocharger shaft (12) of an exhaust gas turbocharger (10) is provided, comprising a housing (18) for enclosing at least a part of the exhaust gas turbocharger shaft (12), at least one rolling bearing (24) for supporting the exhaust gas turbocharger shaft (12) relative to the housing (18), an oil channel (22) formed in the housing (18) for supplying lubricating oil to a radially outwardly facing outer surface (32) of an outer ring (30) of the rolling bearing (24), wherein the outer ring (30) has a projection (44) extending radially outward from the outer surface (32) and the projection (44) is axially spaced from the housing (18) via an axial lubrication gap (46) which communicates fluidically with the oil channel (22) and is provided for damping axial forces.The projection (44) of the outer ring (30) of the rolling bearing (24) allows the axial lubrication gap (46) intended for damping axial forces to be formed cost-effectively and simply, thus enabling a low-noise exhaust gas turbocharger (10) to be built cost-effectively.

Description

[0001] The invention relates to a bearing arrangement with the aid of which an exhaust gas turbocharger shaft of an exhaust gas turbocharger can be mounted, as well as a corresponding exhaust gas turbocharger.

[0002] From EP 3 059 453 A1 an exhaust gas turbocharger for a motor vehicle is known in which a turbocharger shaft is mounted via two oil-lubricated rolling bearings and can run in the axial direction against a housing with a thrust washer fastened to an outer ring of the rolling bearings, wherein lubricating oil can be pressed past a radially outer edge of the thrust washer between axial contact surfaces of the thrust washer and the housing.

[0003] DE 10 2020 134 311 A1 shows a bearing arrangement for supporting an exhaust gas turbocharger shaft of an exhaust gas turbocharger with the features of the preamble of claim 1.

[0004] There is a constant need to reduce noise emissions in a motor vehicle's exhaust gas turbocharger in a cost-effective manner.

[0005] The object of the invention is to demonstrate measures that enable a low-noise exhaust gas turbocharger at low cost.

[0006] The object is achieved according to the invention by a bearing arrangement having the features of claim 1 and an exhaust gas turbocharger having the features of claim 9. Preferred embodiments of the invention are specified in the subclaims and the following description, which can each individually or in combination represent an aspect of the invention, the scope of protection being determined by the claims.

[0007] One aspect of the invention relates to a bearing arrangement for supporting an exhaust gas turbocharger shaft of an exhaust gas turbocharger, comprising a housing for enclosing at least part of the exhaust gas turbocharger shaft, at least one rolling bearing for supporting the exhaust gas turbocharger shaft relative to the housing, an oil channel formed in the housing for supplying lubricating oil to a radially outwardly facing circumferential surface of an outer ring of the rolling bearing, wherein the outer ring has a projection protruding radially outward from the circumferential surface and the projection is axially spaced from the housing via an axial lubrication gap fluidically communicating with the oil channel and provided for damping axial forces, wherein the outer ring has an additional ring protruding from the projection in the axial direction, wherein a radial lubrication gap fluidically communicating with the axial lubrication gap is formed between the additional ring and the housing.In particular, the radial lubrication gap is sealed at one axial end by a sealing element, in particular an O-ring, acting on the additional ring and the housing.

[0008] During normal operation, the exhaust gas turbocharger, and in particular the exhaust gas turbocharger shaft, are subjected to extreme stresses that require a challenging lubrication and cooling concept. For example, it may be necessary to take thermal expansion effects into account by allowing the bearings of the exhaust gas turbocharger shaft to move to a certain extent in the axial direction. However, it has been recognized that unavoidable axial forces in the event of axial compliance in the exhaust gas turbocharger during operation could generate audible acoustic effects. However, the axial lubrication gap can support and dampen any axial forces that occur, thereby preventing structure-borne noise that would otherwise occur. In addition, the axial lubrication gap is not limited by the axial side of the housing that faces the outer surface of the outer ring, but by the axial side of the housing that faces away from the outer surface of the outer ring.This prevents lubricating oil supplied via the oil channel from first having to pass through the projection to fill a lubrication gap. The pressure built up in the axial lubrication gap by the lubricating oil supplied via the oil channel pushes the projection of the outer ring of the rolling bearing away from the oil channel and not towards the oil channel. This ensures that the axial lubrication gap does not collapse to an axial gap width of zero due to the built-up hydraulic pressure, but rather that there is always a sufficient lubricating oil cushion in the axial lubrication gap that can dampen any axial forces that occur. In addition, it is possible for the axial lubrication gap to be limited by the outer ring of the rolling bearing itself and not by an additional component that is first connected to the outer ring. The projection can be formed integrally with the part of the outer ring that forms the outer surface that can be wetted with lubricating oil via the oil channel.This allows the number of components to be kept low and separate connection technology to be eliminated, thus making it possible to reduce manufacturing costs. Furthermore, the housing can have a shape corresponding to the projection, so that the axial lubrication gap is limited in both axial directions and in both radial directions exclusively by the housing and the outer ring of the rolling bearing, as well as any seals provided. This results in a simple, component-saving, and cost-effective design of the axial lubrication gap intended to dampen axial forces. The projection of the outer ring of the rolling bearing allows the axial lubrication gap intended to dampen axial forces to be formed easily and cost-effectively, thus enabling a low-noise exhaust gas turbocharger to be produced cost-effectively.

[0009] The additional ring can provide centering and / or radial support for the outer ring in the housing, similar to the outer ring's lateral surface. Since the additional ring is radially spaced from the outer ring's lateral surface over the extension of the projection, improved support of the outer ring against tilting can be provided. Furthermore, it is possible to intentionally create a radial lubrication gap between the additional ring and the housing, thereby supporting the damping properties of the axial lubrication gap and preferably also providing damping in the radial direction. This can improve vibration damping and reduce noise emissions.

[0010] The exhaust gas turbocharger can be provided in a motor vehicle, for example, to charge fresh air for an internal combustion engine to a higher pressure. Additionally or alternatively, the exhaust gas turbocharger can be driven by exhaust gas at a higher pressure level than the ambient air. Preferably, the exhaust gas turbocharger shaft is coupled to an electric motor so that, depending on the operating situation, electrical energy can be boosted, for example, to overcome turbo lag, or electrical energy can be recuperated that is not required to charge the fresh air, thus eliminating the need to release boost pressure via a wastegate.

[0011] The exhaust turboshaft is specifically designed for extremely high speeds, for example, up to 400,000 rpm. For this purpose, the exhaust turboshaft is made of a ceramic material, for example.

[0012] The rolling bearing is designed for the speeds encountered in exhaust turboshafts. In particular, the outer ring of the rolling bearing has at least one radially extending opening so that lubricating oil can flow from the radially outer surface into the rolling bearing to lubricate and / or cool the rolling bearing. The rolling bearing can have balls, barrels, or needles as rolling elements, which can preferably be accommodated in a bearing cage provided in the radial direction between the outer ring and an inner ring. In particular, the rolling bearing is designed primarily to support bearing forces acting in the radial direction, although the rolling bearing can preferably also be designed to support bearing forces acting in the axial direction to a lesser extent.

[0013] The oil channel can extend from a supply opening formed in the housing, where a lubricating oil supply can be connected, to the circumferential surface of the outer ring of the rolling bearing and to the axial lubrication gap. The oil channel is preferably formed by a plurality of fluidically communicating bores, so that a one-piece boundary of the oil channel is defined by the housing and, if appropriate, by a plug inserted into one end of one of the associated bores. Particularly preferably, the housing has only one supply opening, from which two different bearing assemblies and / or two different rolling bearings in the exhaust gas turbocharger can be supplied with lubricating oil.

[0014] The lubricating oil can be selected based on its tribological properties. However, it is also possible to select the lubricating oil for the purpose of heat dissipation in the exhaust gas turbocharger.

[0015] The axial lubrication gap is primarily designed to dampen axial forces and, if at all, to provide lubrication. It should be noted that relative rotation is not permitted between the outer ring of the rolling bearing and the housing, and a non-rotatable connection between the outer ring and the housing is preferred, obviating the need for lubrication of the surfaces of the outer ring and the housing that face each other. Since the main function of the lubricating oil in the axial lubrication gap is to dampen axial forces, the axial lubrication gap can have a significantly larger gap width than a lubrication gap on an axial plain bearing. For example, the axial gap width b of the axial lubrication gap is 0.1 mm ≤ b ≤ 5.0 mm, in particular 0.5 mm ≤ b ≤ 4.0 mm, and preferably 1.0 mm ≤ b ≤ 3.0 mm.The axial lubrication gap and / or the gap width of the axial lubrication gap is limited, in particular, on one axial side by an axial surface of the housing and on the other axial side by an axial surface of the projection. In particular, the projection, together with the outer ring of the rolling bearing, is in principle axially movable to a limited extent relative to the axial surface of the housing. In theoretical, trouble-free operation without axial forces, a defined initial position of the projection relative to the housing would automatically be established for the gap width of the axial lubrication gap, which represents the reference position for measuring the gap width b of the axial lubrication gap.

[0016] In particular, the oil channel has an axially extending end channel piece with an axially pointing outlet opening opening into the axial lubrication gap, wherein the oil channel in particular has a transverse channel that fluidically communicates with the end channel piece and leads radially to the outer surface of the outer ring. The end channel piece can be easily and inexpensively formed by a bore beginning at the outlet opening to be created. The transverse channel leading to the outer surface of the outer ring can, in turn, branch off from this bore. For example, the transverse channel can be formed by a bore that radially transverses the end channel piece, wherein the part of the bore extending radially outward from the end channel piece can be closed and / or filled by a plug. The axial lubrication gap can be formed at an axial end of the oil channel defined by the outlet opening.

[0017] Preferably, the oil channel, particularly in the flow direction between the transverse channel and the outlet opening, has a throttle for limiting a mass flow of lubricating oil flowing into the axial lubrication gap and / or for providing a damping characteristic for damping axial forces in the axial lubrication gap. The throttle can be used to set a specific ratio of the mass flows of lubricating oil flowing to the circumferential surface of the outer ring on the one hand and into the axial lubrication gap on the other. Furthermore, the pressure in the axial lubrication gap can be influenced, thereby predetermining the damping characteristic of the oil film damping in the axial lubrication gap.

[0018] In particular, the radial lubrication gap is positioned radially outwardly between the housing and the outer surface of the outer ring, wherein the additional ring and the outer surface are provided in different axial regions or partially in a common axial region. One half of the outer ring can have a substantially stepped and / or Z-shaped profile or a substantially U-shaped profile in a sectional view running through the center line of the outer ring in an axial plane. With the stepped profile, the outer ring can be easily manufactured and have a small radial installation space requirement. With a U-shaped profile, the outer ring can encompass part of the housing like a pocket, with a small axial installation space requirement.

[0019] Preferably, the outer ring is supported radially on the housing both via the outer surface and via the additional ring. The additional ring can thus contribute to supporting the radial bearing forces that occur, thereby reducing the loads on the outer surface of the outer ring. This allows for a smaller radial thickness of the outer ring, thus saving installation space.

[0020] Particularly preferably, the outer ring is supported axially and flexibly on the housing via a spring element. This allows the outer ring to compensate for thermal expansion effects. At the same time, the spring element can provide a resilient contribution to damping the axial forces. The spring element is preferably designed to counteract pressure in the axial lubrication gap to prevent excessive axial displacement of the outer ring and to prevent the gap width of the axial lubrication gap from becoming too large.

[0021] In particular, an annular gap formed between the housing and the circumferential surface of the outer ring and fluidly communicating with the oil channel is sealed from the axial lubrication gap by a sealant, in particular an O-ring. The annular gap can be filled with lubricating oil from the oil channel, in particular via the transverse channel, and can provide a reservoir from which lubricating oil can flow into the interior of the rolling bearing and / or support heat dissipation from the rolling bearing.

[0022] A further aspect relates to an exhaust gas turbocharger for a motor vehicle, comprising an exhaust gas turbocharger shaft mounted on a first bearing point and a second bearing point, wherein the first bearing point and / or the second bearing point has a bearing arrangement which can be designed and further developed as described above, and preferably a supply opening which communicates fluidly with the oil channel for connecting a lubricating oil supply, in particular a pressure-lubricated one. The exhaust gas turbocharger can be designed and further developed, in particular as explained above with reference to the bearing arrangement. The axial lubrication gap provided for damping axial forces can be formed cost-effectively and easily by means of the projection of the outer ring of the rolling bearing, thus enabling a low-noise exhaust gas turbocharger to be produced cost-effectively.

[0023] Preferably, the exhaust gas turbocharger shaft forms a rotor shaft of a rotor of an electric machine. This allows the electric machine to be integrated, in particular, into the housing of the exhaust gas turbocharger without the need to connect a separate electric machine located outside the housing of the exhaust gas turbocharger. Since a sufficient seal can be formed between the outer ring of the rolling bearing and the housing, there is no risk of lubricating oil penetrating the interior of the electric machine. Adequate operational reliability of the electric machine can be ensured.

[0024] The invention will be explained below by way of example with reference to the accompanying drawings using preferred embodiments, wherein the features presented below can represent an aspect of the invention both individually and in combination, the scope of protection being determined by the claims. They show: Fig. 1 a schematic simplified sectional view of an exhaust gas turbocharger and Fig. 2 a schematic sectional detailed view of the bearing arrangement according to the invention for the exhaust gas turbocharger from Fig. 1.

[0025] The Fig. The exhaust gas turbocharger 10 shown in Figure 1 can be used in a motor vehicle for charging fresh air supplied to an internal combustion engine, wherein the exhaust gas turbocharger 10 can be driven in particular by the exhaust gas coming from the internal combustion engine. The exhaust gas turbocharger 10 has an exhaust gas turbocharger shaft 12, which can be mounted and supported in a housing 18 of the exhaust gas turbocharger 10 with the aid of a first bearing arrangement 14 and a second bearing arrangement 16. The housing 18 has, in particular at the highest point in the direction of gravity, a supply opening 20, via which lubricating oil can be transferred to oil channels 22 leading to the respective bearing arrangement 14, 16 in order to lubricate and / or cool the bearing arrangements 14, 16. The respective oil channel 22 can be composed of a plurality of bores, in particular closed at one end with a plug.

[0026] As in Fig. 2 is shown in detail on one of the bearing assemblies 14, 16 by way of example, the respective bearing assembly 14, 16 has a rolling bearing 24. The rolling bearing 24 has an inner ring 26 connected to the exhaust gas turbocharger shaft 12, which can rotate relative to an outer ring 30 via a rolling element 28, which is designed, for example, as a ball. The outer ring 30 has a radially outward-facing circumferential surface 32 to which lubricant can be conveyed from the oil channel 22, wherein in particular the lubricant can reach the interior of the rolling bearing 24 from the circumferential surface 32 through the outer ring 30 in order to lubricate the rolling element 28. For this purpose, the oil channel 22 can have an end channel piece 36 ending at an outlet opening 34, with which a transverse channel 38 is fluidically connected in order to guide the lubricating oil to the outer surface 32 of the outer ring 30.An annular gap 40 is formed between a radially inwardly facing inner side of the housing 18 and the lateral surface 32, which is axially delimited at each of its axial ends by a sealing means 42 designed as an O-ring.

[0027] The outer ring 30 has a projection 44 projecting radially outward from the circumferential surface 32, which is axially spaced from the outlet opening 34 of the oil channel 22 and thereby maintains an axial lubrication gap 46 between the housing 18 and the projection 44. A throttle 48 is provided in the end channel section 36 of the oil channel 22 between the transverse channel 38 and the outlet opening 34, through which a throttled mass flow of lubricating oil flows into the axial lubrication gap 46 to dampen axial forces and axial vibrations. With the aid of a spring element 50 subjected to compressive and / or tensile stress, the outer ring 30 can be resiliently connected and / or supported to the housing 18 in the axial direction. The spring element 50 can also absorb and temporarily store axial forces and influence the axial gap width of the axial lubrication gap 46.

[0028] In the illustrated embodiment, an additional ring 52 protrudes from the projection 44 in the axial direction, wherein the projection 44 and the additional ring 52 are formed integrally with the rest of the outer ring 30. In the illustrated embodiment, the additional ring 52 protrudes away from the outer surface 32, resulting in a stepped profile for the outer ring 30. Alternatively, the additional ring 52 can protrude from the projection 44 in the opposite direction and encompass the correspondingly adapted housing 18 in a U-shape. In both variants, it is possible for a radial lubrication gap 54 to be formed between the housing 18 and the additional ring 52, which is fluidically connected to the axial lubrication gap 46 and is sealed at one axial end by a sealing element 56 designed as an O-ring.

[0029] In a further preferred embodiment, the exhaust gas turbocharger shaft, as in Fig.1, may be part of a rotor 58, which interacts with a stator 60 to form an electric machine 62. The electric machine can be operated, in particular, in motor mode and / or generator mode. The electric machine is formed entirely within the housing 18 and is thus integrated into the exhaust gas turbocharger 10.

Claims

[1] Bearing arrangement (14, 16) for supporting an exhaust gas turbocharger shaft (12) of an exhaust gas turbocharger (10), with a housing (18) for enclosing at least part of the exhaust gas turbocharger shaft (12), at least one rolling bearing (24) for supporting the exhaust gas turbocharger shaft (12) relative to the housing (18), an oil channel (22) formed in the housing (18) for supplying lubricating oil to a radially outwardly facing surface (32) of an outer ring (30) of the rolling bearing (24), wherein the outer ring (30) has a projection (44) projecting radially outward from the lateral surface (32) and the projection (44) is axially spaced from the housing (18) via an axial lubrication gap (46) fluidically communicating with the oil channel (22) and provided for damping axial forces characterized by , that the outer ring (30) has an additional ring (52) projecting from the projection (44) in the axial direction, wherein a radial lubrication gap (54) fluidically communicating with the axial lubrication gap (46) is formed between the additional ring (52) and the housing (18). [2] Bearing arrangement (14, 16) according to claim 1, wherein the oil channel (22) has an end channel piece (36) extending in the axial direction with an outlet opening (34) pointing in the axial direction and opening into the axial lubrication gap (46), wherein the oil channel (22) has a transverse channel (38) fluidically communicating with the end channel piece (36) and leading to the lateral surface (32) of the outer ring (30) in the radial direction. [3] Bearing arrangement (14, 16) according to claim 1 or 2, wherein the oil channel (22) has a throttle (48) for limiting a mass flow of the lubricating oil flowing into the axial lubrication gap (46) and / or for providing a damper characteristic for damping axial forces in the axial lubrication gap (46). [4] Bearing arrangement (14, 16) according to one of claims 1 to 3, wherein the radial lubrication gap (54) is sealed at one axial end by a sealing element (56) engaging the additional ring (52) and the housing (18). [5] Bearing arrangement (14, 16) according to claim 4, wherein the radial lubrication gap (54) is positioned offset radially outwardly between the housing (18) and the lateral surface (32) of the outer ring (30), wherein the additional ring (52) and the lateral surface (32) are provided in different axial regions or partially in a common axial region. [6] Bearing arrangement (14, 16) according to claim 4 or 5, wherein a support of the outer ring (52) in the radial direction on the housing (18) is formed both via the lateral surface (32) and via the additional ring (52). [7] Bearing arrangement (14, 16) according to one of claims 1 to 6, wherein the outer ring (30) is supported in an axially yielding manner on the housing (18) via a spring element (50). [8] Bearing arrangement (14, 16) according to one of claims 1 to 7, wherein an annular gap (40) formed between the housing (18) and the circumferential surface (32) of the outer ring (30) and fluidically communicating with the oil channel (22) is sealed off from the axial lubrication gap (46) by a sealing means (42). [9] Exhaust gas turbocharger (10) for a motor vehicle, with an exhaust gas turbocharger shaft (12) mounted on a first bearing point and on a second bearing point, wherein the first bearing point and / or the second bearing point has a bearing arrangement (14, 16) according to one of claims 1 to 8, and a supply opening (20) fluidly communicating with the oil channel (22) for connecting a lubricating oil supply. [10] Exhaust gas turbocharger (10) according to claim 9, wherein the exhaust gas turbocharger shaft (12) forms a rotor shaft of a rotor (58) of an electric machine (62).

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